In-Line Bit Interleaved Serially Concatenated Coded Modulation

Doctoral thesis, 2007

A communication system using in-line bit interleaved serially concatenated trellis coded modulation (SCTCM) over the additive white Gaussian noise (AWGN) channel is investigated. In-line bit interleaving refers to an interleaving method for which the random bit interleaver is divided into several independent constituent bit interleavers. Normally, an in-line bit interleaved serially concatenated code consists of a rate r_o=k_o/n_o outer code, followed by n_o separate bit interleavers whose outputs are fed to a rate r_i=k_i/n_i inner code, where n_o=k_i. Unlike conventional random bit interleaving, the input and output sequences of an in-line bit interleaver are not entirely decoupled. Hence, previously known code design principles for serially concatenated codes cannot be directly applied to this code structure. Some code design methods, such as curve matching by using extrinsic information transfer (EXIT) analysis, completely rely on properties that require conventional random bit interleaving. The objective of this thesis is therefore to develop a new code design methodology for in-line bit interleaved serially concatenated codes and design new in-line bit interleaved SCTCM systems. Design guidelines are introduced for both the inner and outer codes. As inner code we investigate both recursive and non-recursive convolutional codes. It is shown - perhaps somewhat surprisingly - that non-recursive inner codes sometimes may be preferable over recursive inner codes. The simulated bit error rate (BER) performance indicates that SCTCM systems using in-line bit interleaving outperforms SCTCM systems with conventional bit interleaving. Simulation results are obtained for various throughputs and signal constellations. In particular, a communication system with a throughput of 2 bits/symbol and 8PSK modulation is considered throughout the thesis.